U.S. patent application number 14/876690 was filed with the patent office on 2016-07-28 for harq design for high performance wireless backhaul.
This patent application is currently assigned to TEXAS INSTRUMENTS INCORPORATED. The applicant listed for this patent is TEXAS INSTRUMENTS INCORPORATED. Invention is credited to PIERRE BERTRAND, JUNE CHUL ROH, JUN YAO.
Application Number | 20160218849 14/876690 |
Document ID | / |
Family ID | 56417850 |
Filed Date | 2016-07-28 |
United States Patent
Application |
20160218849 |
Kind Code |
A1 |
BERTRAND; PIERRE ; et
al. |
July 28, 2016 |
HARQ DESIGN FOR HIGH PERFORMANCE WIRELESS BACKHAUL
Abstract
A method of operating a wireless communication system is
disclosed. The method includes receiving respective downlink
transmissions at N second transceivers from a first transceiver,
where N is a positive integer greater than 1. The reception
acknowledgement signals by the N second transceivers are combined
into a single reception acknowledgement signal and transmitted to
the first transceiver.
Inventors: |
BERTRAND; PIERRE; (Antibes,
FR) ; ROH; JUNE CHUL; (Allen, TX) ; YAO;
JUN; (Shanghai, CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TEXAS INSTRUMENTS INCORPORATED |
DALLAS |
TX |
US |
|
|
Assignee: |
TEXAS INSTRUMENTS
INCORPORATED
DALLAS
TX
|
Family ID: |
56417850 |
Appl. No.: |
14/876690 |
Filed: |
October 6, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62106604 |
Jan 22, 2015 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04L 5/001 20130101;
H04L 2001/0093 20130101; H04L 2001/0097 20130101; H04L 1/1607
20130101; H04L 5/1469 20130101; H04L 1/1621 20130101; H04L 5/14
20130101; H04L 1/1896 20130101; H04L 5/0055 20130101 |
International
Class: |
H04L 5/00 20060101
H04L005/00; H04W 72/08 20060101 H04W072/08; H04W 72/00 20060101
H04W072/00; H04W 72/04 20060101 H04W072/04; H04L 5/14 20060101
H04L005/14 |
Claims
1. A method of operating a wireless communication system,
comprising: receiving N downlink transmissions at a second
transceiver from a first transceiver, where N is a positive integer
greater than 1; combining reception acknowledgement signals for the
respective N downlink transmissions into a single reception
acknowledgement signal; and transmitting the single reception
acknowledgement signal to the first transceiver, wherein N is
independently configured by the first transceiver for the second
transceiver.
2. The method of claim 1, wherein first transceiver is a hub unit
(HU) of a wireless backhaul system, and wherein the second
transceiver is a remote unit (RU) of the wireless backhaul
system.
3. The method of claim 1, wherein N is configured in response to a
channel quality between the first transceiver and a respective one
of the second transceivers.
4. The method of claim 1, wherein the downlink transmissions are
received on a Physical Downlink Shared Channel (PDSCH), and wherein
the single reception acknowledgement signal is transmitted on a
Physical Uplink Control Channel (PUCCH).
5. The method of claim 1, wherein the single reception
acknowledgement signal is an acknowledgement (ACK) when all N
downlink transmissions are correctly received at the second
transceiver, and wherein the single reception acknowledgement
signal is a negative acknowledgement (NACK) when at least one of
the N downlink transmissions is incorrectly received at the second
transceiver.
6. The method of claim 1, comprising: receiving incorrectly a
respective downlink transmission having a first allocation size at
one of the second transceivers; and receiving a retransmission of
the incorrect downlink transmission having a second allocation
size.
7. The method of claim 6, comprising rate matching the
retransmission to the second allocation size.
8. The method of claim 1, wherein the downlink transmissions occur
within a feedback window determined by a time division duplex (TDD)
downlink/uplink frame configuration and uplink slot number of the
TDD frame.
9. The method of claim 8, wherein N is signaled to a second
transceiver in a Physical Broadcast Channel (PBCH) within the
feedback window.
10. The method of claim 8, wherein the feedback window spans a
plurality of time slots of a frame and a plurality of component
carrier frequencies.
11. The method of claim 1, wherein the N acknowledgement signals
are combined in order of sequential time slots and component
carrier frequencies.
12. A method of operating a wireless communication system,
comprising: receiving respective uplink transmissions at a first
transceiver from M second transceivers, where M is a positive
integer greater than 1; combining reception acknowledgement signals
for the respective M second transceivers into a single reception
acknowledgement signal; and transmitting the single reception
acknowledgement signal to each of the M second transceivers.
13. The method of claim 12, wherein first transceiver is a hub unit
(HU) of a wireless backhaul system, and wherein the M second
transceivers are remote units (RUs) of the wireless backhaul
system.
14. The method of claim 12, wherein the uplink transmissions are
received on a Physical Downlink Shared Channel (PUSCH), and wherein
the single reception acknowledgement signal is transmitted on a
Physical HARQ Indicator Channel (PHICH).
15. The method of claim 12, comprising receiving respective
retransmitted uplink transmissions from the M second transceivers
when at least one of the reception acknowledgement signals is
negative (NACK).
16. A method of operating a wireless communication system,
comprising: transmitting downlink control information (DCI) from a
first transceiver to a second transceiver indicating parameters for
one of an uplink (UL) and downlink (DL) transmission; and
transmitting a preempt signal with the control information to
indicate whether said transmission is preempted by one of an UL and
DL retransmission.
17. The method of claim 16, wherein the preempt bit has a first
logic state for a retransmission of a previous transmission and the
DCI indicates a format of the retransmission.
18. The method of claim 16, wherein the preempt bit has a second
logic state when no second transceiver served by the first
transceiver is scheduled for said one of an UL and DL
transmission.
19. The method of claim 16, wherein the DCI from the first
transceiver is all zero when no second transceiver served by the
first transceiver is scheduled for said one of an UL and DL
transmission.
20. The method of claim 16, comprising: scheduling the second
transceiver for said one of an UL and DL transmission in a dynamic
allocation; receiving a negative acknowledgement signal for the
scheduling from the second transceiver; setting the DCI from the
first transceiver to all zero; and setting the preempt bit to a
first logic state.
Description
[0001] This application claims the benefit under 35 U.S.C.
.sctn.119(e) of Provisional Appl. No. 62/106,604, filed Jan. 22,
2015 (TI-75798PS), which is incorporated herein by reference in its
entirety.
BACKGROUND OF THE INVENTION
[0002] Embodiments of the present invention relate to wireless
communication systems and, more particularly, to low overhead
control signaling of a Non-Line-Of-Sight (NLOS) wireless
communication system compatible with a time-division duplex long
term evolution (TD-LTE) Radio Access Network (RAN).
[0003] A key answer to the huge data demand increase in cellular
networks is the deployment of small cells providing Long Term
Evolution (LTE) connectivity to a smaller number of users than the
number of users typically served by a macro cell. This allows both
providing larger transmission/reception resource opportunities to
users as well as offloading the macro network. However, although
the technical challenges of the Radio Access Network (RAN) of small
cells have been the focus of considerable standardization effort
through 3GPP releases 10-12, little attention was given to the
backhaul counterpart. It is a difficult technological challenge,
especially for outdoor small cell deployment where wired backhaul
is usually not available. This is often due to the non-conventional
locations of small cell sites such as lamp posts, road signs, bus
shelters, etc., in which case wireless backhaul is the most
practical solution.
[0004] The LTE wireless access technology, also known as Evolved
Universal Terrestrial Radio Access Network (E-UTRAN), was
standardized by the 3GPP working groups. OFDMA and SC-FDMA (single
carrier FDMA) access schemes were chosen for the DL and UL of
E-UTRAN, respectively. User equipments (UEs) are time and frequency
multiplexed on a physical uplink shared channel (PUSCH) and a
physical uplink control channel (PUCCH), and time and frequency
synchronization between UEs guarantees optimal intra-cell
orthogonality. The LTE air-interface provides the best
spectral-efficiency and cost trade-off of recent cellular networks
standards, and as such, has been vastly adopted by operators as the
unique 4G technology for the Radio Access Network (RAN), making it
a robust and proven technology. As the tendency in the RAN topology
is to increase the cell density by adding small cells in the
vicinity of a legacy macro cells, the associated backhaul link
density increases accordingly and the difference between RAN and
backhaul wireless channels also decreases. This also calls for a
point-to-multipoint (P2MP) backhaul topology. As a result,
conventional wireless backhaul systems typically employing single
carrier waveforms with time-domain equalization (TDE) techniques at
the receiver become less practical in these environments. This is
primarily due to their limitation of operating in point-to-point
line-of-sight (LOS) channels in the 6-42 GHz microwave frequency
band. On the contrary, the similarities between the small cell
backhaul and small cell access topologies (P2MP) and wireless radio
channel (NLOS) naturally lead to use a very similar air
interface.
[0005] There are several special issues associated with NLOS
backhaul links at small cell sites, such as a requirement for high
reliability with a packet error rate (PER) of 10.sup.-6, sparse
spectrum availability, critical latency, cost, and relaxed
peak-to-average power ratio (PAPR). Behavior of NLOS backhaul links
at small cell sites also differs from RAN in that there is no
handover, remote units do not connect and disconnect at the same
rate as user equipment (UE) and the NLOS remote unit (RU) and small
cell site is not mobile. Moreover, typical NLOS backhaul systems do
not support Hybrid Automatic Repeat Request (HARQ) transmissions to
confirm reception of UL and DL transmissions.
[0006] While preceding approaches provide improvements in backhaul
transmission in a wireless NLOS environment, the present inventors
recognize that still further improvements are possible.
Accordingly, the preferred embodiments described below are directed
toward this as well as improving upon the prior art.
BRIEF SUMMARY OF THE INVENTION
[0007] In a first embodiment of the present invention, there is
disclosed a method of operating a wireless communication system.
The method includes receiving N respective downlink transmissions
at a second transceiver from a first transceiver, where N is a
positive integer greater than 1. Reception acknowledgement signals
(ACK/NACKs) for the N downlink transmissions are combined into a
single reception acknowledgement signal. The single reception
acknowledgement signal is transmitted to the first transceiver. The
first transceiver configures N independently for each of a
plurality of transceivers including the second transceiver.
[0008] In a second embodiment of the present invention, there is
disclosed a method of operating a wireless communication system.
The method includes receiving respective uplink transmissions at a
first transceiver from M second transceivers, where M is a positive
integer greater than 1. Reception acknowledgement signals
(ACK/NACKs) for the M second transceivers are combined into a
single reception acknowledgement signal. The single reception
acknowledgement signal is transmitted to each of the M second
transceivers.
[0009] In a third embodiment of the present invention, there is
disclosed a method of operating a wireless communication system.
The method includes transmitting control information from a first
transceiver to a second transceiver indicating parameters for one
of an uplink (UL) and downlink (DL) transmission. A preempt signal
is transmitted with the control information to indicate whether a
first transmission is preempted by one of an uplink (UL) and
downlink (DL) transmission.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0010] FIG. 1 is a diagram of a wireless communication system with
a cellular macro site hosting a backhaul point to multipoint (P2MP)
hub unit (HU) serving plural remote units (RUs) which relay
communications between small cells and plural user equipment
(UE);
[0011] FIG. 2 is a diagram of downlink and uplink subframe
configurations according to the present invention;
[0012] FIG. 3 is a diagram of a subset of downlink and uplink
subframe configurations of the prior art;
[0013] FIG. 4 is a diagram of a subset of downlink and uplink slot
configurations according to the present invention;
[0014] FIG. 5 is a detailed diagram of a data frame as in
configuration 3 (FIG. 2) showing downlink and uplink slots and a
special slot;
[0015] FIG. 6 is a diagram of a downlink (DL) slot that may be used
in the data frame of FIG. 5 according to the present invention;
[0016] FIG. 7 is a diagram of an uplink (UL) slot that may be used
in the data frame of FIG. 5 according to the present invention;
[0017] FIG. 8A is a diagram showing RU allocation for frame
configuration 6 of FIG. 2;
[0018] FIG. 8B is a diagram showing ACK/NACK remote unit (RU)
bundling transmitted in the PUCCH for the allocation of FIG. 8A;
and
[0019] FIG. 9 is a diagram showing non-adaptive retransmissions
having different allocation sizes through rate matching.
DETAILED DESCRIPTION OF THE INVENTION
[0020] Some of the following abbreviations are used throughout the
instant specification. The following glossary provides an
alphabetical explanation of these abbreviations.
[0021] BLER: Block Error Rate
[0022] CQI: Channel Quality Indicator
[0023] CRS: Cell-specific Reference Signal
[0024] CSI: Channel State Information
[0025] CSI-RS: Channel State Information Reference Signal
[0026] DCI: Downlink Control Information
[0027] DL: DownLink
[0028] DwPTS: Downlink Pilot Time Slot
[0029] eNB: E-UTRAN Node B or base station or evolved Node B
[0030] EPDCCH: Enhanced Physical Downlink Control Channel
[0031] E-UTRAN: Evolved Universal Terrestrial Radio Access
Network
[0032] FDD: Frequency Division Duplex
[0033] HARQ: Hybrid Automatic Repeat Request
[0034] HU: (backhaul) Hub Unit
[0035] ICIC: Inter-cell Interference Coordination
[0036] LTE: Long Term Evolution
[0037] MAC: Medium Access Control
[0038] MIMO: Multiple-Input Multiple-Output
[0039] MCS: Modulation Control Scheme
[0040] OFDMA: Orthogonal Frequency Division Multiple Access
[0041] PCFICH: Physical Control Format Indicator Channel
[0042] PAPR: Peak-to-Average Power Ratio
[0043] PDCCH: Physical Downlink Control Channel
[0044] PDSCH: Physical Downlink Shared Channel
[0045] PMI: Precoding Matrix Indicator
[0046] PRB: Physical Resource Block
[0047] PRACH: Physical Random Access Channel
[0048] PS: Pilot Signal
[0049] PUCCH: Physical Uplink Control Channel
[0050] PUSCH: Physical Uplink Shared Channel
[0051] QAM: Quadrature Amplitude Modulation
[0052] RAR: Random Access Response
[0053] RE: Resource Element
[0054] RI: Rank Indicator
[0055] RRC: Radio Resource Control
[0056] RU: (backhaul) Remote Unit
[0057] SC-FDMA: Single Carrier Frequency Division Multiple
Access
[0058] SPS: Semi-Persistent Scheduling
[0059] SRS: Sounding Reference Signal
[0060] TB: Transport Block
[0061] TDD: Time Division Duplex
[0062] TTI: Transmit Time Interval
[0063] UCI: Uplink Control Information
[0064] UE: User Equipment
[0065] UL: UpLink
[0066] UpPTS: Uplink Pilot Time Slot
[0067] Referring to FIG. 1, there is a NLOS Time Division Duplex
(TDD) wireless backhaul system according to the present invention.
Cellular macro site 100 hosts a macro base station. Macro site 100
also hosts a wireless backhaul hub unit (HU). Macro site 100 is
connected with small cell sites such as small cell site 104. Each
small cell site is co-located with a small cell base station and
wireless backhaul remote unit (RU). Macro site 100 communicates
with the small cell sites through a point-to-multipoint (P2MP)
wireless backhaul system via backhaul links such as backhaul link
110. The base station of macro site 100 communicates directly with
UE 102 over RAN link 112. UE 106, however, communicates directly
with the small cell base station of small cell site 104 over a RAN
access link 108. The RU of small cell site 104, in turn,
communicates directly with the HU of macro cell site 100 over a
backhaul link 110. The system is designed to maximize spectrum
reuse. The backhaul link 110 design utilizes a 0.5 ms slot-based
transmission time interval (TTI) to minimize latency and 5 ms UL
and DL frames for compatibility with TD-LTE. Thus, various UL/DL
ratios are compatible with TD-LTE configurations. This allows
flexible slot assignment for multiple Remote Units (RUs).
[0068] FIG. 2 shows the TDD frame structure of the present
invention, with seven uplink (UL) and downlink (DL) frame
configurations, thus supporting a diverse mix of UL and DL traffic
ratios. Each configuration includes various uplink (U), downlink
(D), and special (S) slots, each having a 0.5 ms duration transmit
time interval (TTI) for a total frame duration of 5 ms. In one
embodiment, this frame structure is utilized to generate an NLOS
backhaul link 110 of FIG. 1. However, the present invention may be
used to generate any kind of communication link sharing similar
co-existence with TD-LTE and performance requirements as the NLOS
backhaul link. As a result, without loss of generality the frame
structure and associated components (slots, channels, etc. . . . )
of the present invention are referred to as "NLOS backhaul" or
simply "NLOS" frame, slots, channels, etc.
[0069] Referring now to FIG. 3, the frame structure of a 10 ms
TD-LTE frame of the prior art will be compared to a 5 ms TDD frame
(FIG. 4) of the present invention. FIG. 4 is a more detailed view
of UL/DL frame configurations 1, 3 and 5 as shown at FIG. 2. The
frame of FIG. 3 is divided into ten subframes, each subframe having
a 1 ms TTI. Each subframe is further divided into two slots, each
slot having a 0.5 ms duration. Thus, there are twenty slots (0-19)
in each TD-LTE configuration. A D in a slot indicates it is a
downlink slot. Correspondingly, a U in a slot indicates it is an
uplink slot. Time slots 2 and 3 constitute a special subframe
allowing transitioning from a DL subframe to an UL subframe. DwPTS
and UpPTS indicate downlink and uplink portions of the special
subframe, respectively.
[0070] By way of comparison, the frame of FIG. 4 of the present
invention has a 5 ms duration and is slot based rather than
subframe based. Each frame has ten (0-9) slots. Each slot has a 0.5
ms duration. As with the frame of FIG. 3, D indicates a downlink
slot, and U indicates an uplink slot. In each of the three UL/DL
configurations of FIG. 4, however, slots 3 of both frames include a
special slot indicated by an S, rather than the special subframes
in slots 2-3 and 12-13 of FIG. 3. This fixed location of the
special slot assures compatibility with TD-LTE frames. It
advantageously permits always finding an NLOS UL/DL configuration
that is 100% compatible with any 5 ms period TD-LTE UL/DL subframe
configuration. For example, this prevents an NLOS backhaul DL
transmission from interfering with a TD-LTE RAN UL transmission on
an access link when both operate on the same frequency. In other
words, it advantageously prevents the transmitter at macro cell
site 100 of one system from interfering with the receiver of a
co-located system.
[0071] The frame configurations of FIG. 4 have several features in
common with the frame configurations of FIG. 3 to assure
compatibility when operating at the same frequency. Both frames
have 0.5 ms slot duration with seven SC-FDMA symbols and a normal
cyclic prefix (CP) in each slot. The SC-FDMA symbol duration is the
same in each frame. Both frames have the same number of subcarriers
for respective 5 MHz, 10 MHz, 15 MHz, and 20 MHz bandwidths, and
both have 15 kHz subcarrier spacing. Both frames use the same
resource element (RE) definition and support 4, 16, and 64 QAM
encoding.
[0072] The frame configuration of FIG. 4 has several unique
features. The symbols of each slot are primarily SC-FDMA for both
UL and DL. The first SC-FDMA symbol of each slot includes a pilot
signal (PS) to improve system latency. A cell-specific sync signal
(SS) different from the PS is included in each frame for cell
search and frame boundary detection.
[0073] Referring now to FIG. 5, there is a detailed diagram of an
NLOS backhaul (BH) frame as shown in UL/DL configuration 3 of FIG.
4. Here and in the following discussion, the vertical axis of the
diagram indicates frequencies of component carriers, and the
horizontal axis indicates time, where each slot has 0.5 ms
duration. For example, a slot having a 20 MHz bandwidth includes
1200 subcarriers (SC) having a carrier spacing of 15 kHz. The frame
includes DL slots, a special slot, and UL slots. Each DL and UL
slot has seven respective single carrier frequency division
multiple access (SC-FDMA) symbols. Each symbol is indicated by a
separate vertical column of the slot.
[0074] Referring to FIG. 6, there is a detailed diagram of a
downlink slot that may be used with the frame of FIG. 5. DL slots
are used for transmitting the Physical Downlink Shared Channel
(PDSCH) conveying payload traffic from the HU to the RUs. The DL
slot includes dynamic and semi-persistent scheduling (SPS) regions
as directed by Medium Access Control (MAC) signaling. Dynamic
scheduling allocates resources based on UE feedback about the link
condition. This achieves flexible resource allocation at the cost
of increased control signaling that may hinder packet delivery.
Semi-persistent scheduling allocates packets for a fixed future
time. This advantageously provides flexible resource allocation
with fewer control signals. With the exception of special slots,
the DL slot also contains the Physical HARQ Indicator Channel
(PHICH) conveying HARQ ACK/NACK feedback to the RU. The Physical
Downlink Control Channel (PDCCH) is also transmitted in this slot.
The PDCCH provides the RU with PHY control information for MCS and
MIMO configuration for each dynamically scheduled RU in that slot.
The PDCCH also provides the RU with PHY control information for MCS
and MIMO configuration for each dynamically scheduled RU in one or
more future UL slots.
[0075] In order to improve the latency for high priority packets,
four pairs of spectrum allocations at both ends of the system
bandwidth may be assigned to different RUs, where the frequency gap
between the two allocation chunks of a pair is the same across
allocation pairs. The resource allocation is done in a
semi-persistent scheduling (SPS) approach through a dedicated
message from higher layers in the PDSCH channel. The size of each
SPS allocation pair is configurable depending on expected traffic
load pattern. For example, no physical resource blocks (PRBs) are
allocated for SPS transmission when there is no SPS allocation.
With greater expected traffic, either two (one on each side of the
spectrum) or four (two on each side of the spectrum) PRBs may be
allocated. Each RU may have any SPS allocation or multiple adjacent
SPS allocations. In one embodiment, all four SPS allocation pairs
are the same size. Most remaining frequency-time resources in the
slot, except for PS, PDCCH, PHICH, and SPS allocations, are
preferably dynamically assigned to a single RU whose scheduling
information is conveyed in the PBCH.
[0076] Similar to LTE, in order to minimize the complexity, all
allocation sizes are multiples of PRBs (12 subcarriers) and are
restricted to a defined size set. The only exception is for SPS
allocations that may take the closest number of sub-carriers to the
nominal targeted allocation size (2 or 4 PRBs). This minimizes the
wasted guard bands between SPS and the PDSCH or PUSCH.
[0077] A special slot structure is disclosed which includes a Sync
Signal (SS), Physical Broadcast Channel (PBCH), Pilot Signals (PS),
Guard Period (GP), and Physical Random Access Channel (PRACH) as
will be described in detail. These slot-based features greatly
simplify the LTE frame structure, reduce cost, and maintain
compatibility with TD-LTE. The present invention advantageously
employs a robust Forward Error Correction (FEC) method by
concatenating turbo code as an inner code with a Reed Solomon outer
block code providing a very low Block Error Rate (BLER). Moreover,
embodiments of the present invention support carrier aggregation
with up to four Component Carriers (CCs) per HU with dynamic
scheduling of multiple RUs with one dynamic allocation per CC.
These embodiments also support semi-persistent scheduling (SPS) of
small allocations in Frequency Division Multiple Access (FDMA)
within a slot for RUs destined to convey high priority traffic,
thereby avoiding latency associated with Time Division Multiple
Access (TDMA) of dynamic scheduling. This combination of TDMA
dynamic scheduling and FDMA SPS provides optimum performance with
minimal complexity.
[0078] There are several advantages to this type of dynamic
allocation. Each RU receives the allocation information from the
parent HU on the physical broadcast channel (PBCH). Each RU decodes
this allocation information every 5 ms to find its potential
slot(s) and component carrier(s). In this manner, every RU is aware
of the dynamic slot allocation for every other RU served by the HU.
Each RU then obtains procedural information on a physical downlink
control channel (PDCCH) identified with the respective slot. In
other words, the PDCCH provides procedural information such as
modulation control scheme (MCS), precoding matrix indicator (PMI),
and Rank Indicator (RI) without regard to which RU is the intended
recipient of that slot. The benefit of this is that the PDCCH may
be distributed to all DL slots and component carriers with a
minimal size. Each PDCCH does not need to carry an index of the RU
scheduled in its associated slot. Moreover, since all RU indices
and component carriers are identified by the PBCH, receipt of all
allocation information may be acknowledged by each RU with a single
PBCH-ACK.
[0079] FIG. 7, there is a detailed diagram of the uplink slot that
may be used with the frame of FIG. 5. UL slots are used for
transmitting the Physical Uplink Shared Channel (PUSCH) conveying
payload traffic to the HU from the RUs. The PUSCH region in FIG. 7
includes both dynamic and semi-persistent scheduling (SPS)
allocations, where the latter are located at both spectrum edges of
the PUSCH region as shown in FIG. 5. The PUCCH provides the HU with
HARQ ACK/NACK feedback from the RU. ACK/NACK bundling is needed in
some configurations, and bundling must apply per RU. A direct
consequence is that ACK/NACK mapping onto PUCCH resources group
ACK/NACKs on a per RU basis. This assumes each RU is aware of all
DL allocations of other RUs. For dynamic allocations, this is
straightforward since each RU decodes all dynamic grants in the
PBCH. For SPS allocations, this implies higher layers signal SPS
allocations of all RUs to each RU. In case of ACK/NACK bundling,
each RU is aware of the potential bundling factor applied to all
other RUs, so each RU is aware of the total number
N.sub.RU.sup.A/N(n.sub.RU) of PDSCH ACK/NACKs (bundled or not)
reported by any given RU with RU index n.sub.RU. For each RU, the
PDSCH ACK/NACKs to be transmitted in a PUCCH slot are first grouped
in the time direction across multiple DL slots associated with the
UL slot in chronological order. Then they are grouped in the
frequency direction across secondary component carriers (CCs) first
by decreasing CC index and then by primary CC last. In the primary
CC they are grouped first across the dynamic allocation and then
the SPS allocation. With dynamic scheduling, the RU decodes the
PBCH every 5 ms to find its potential slot allocation information.
Transmission over the PUSCH or reception over the PDSCH may be
dynamically or semi-persistently scheduled (SPS) by the HU. Both
PUSCH transmission and PDSCH reception are configured independently
for each RU through higher layer signaling on the PDSCH. RUs with
good channel characteristics may be configured with larger bundling
factors than RUs with poor channel characteristics. The SPS
configuration includes frequency chunk(s) among four available SPS
chunks per slot as well as a number of adjacent chunks used by a
RU. Additional configuration information includes time slot(s) in
each frame, period of the SPS allocation, modulation control scheme
(MCS), transmission mode (TM), and SPS chunk size for DL.
[0080] PUCCH allocation size is mainly driven by PDSCH ACK/NACK
allocation. For a given bandwidth, only a fixed number of physical
resource blocks (PRBs) are available for PUCCH and PUSCH
transmission. According to an embodiment of the present invention,
a number of PUCCH PRBs is completely determined from the UL/DL
frame configuration, the slot number, and the number of RUs
supported by the HU. As a result, the PUCCH allocation size does
not need to be explicitly signaled to the RUs. Each RU determines
the PUCCH allocation size for each slot from the frame
configuration and the total number of RUs.
[0081] By way of example, FIG. 8A is a diagram showing DL slot
allocation for RUs (0-4) for frame configuration 6 of FIG. 2. The
diagram is organized by row according to frequency with the lower
five rows for primary component carrier (0) and the upper three
rows (1-3) for secondary component carriers. The component carriers
are identified as dynamic or SPS allocations in the second column.
Each of the dynamic or SPS allocations is further identified with a
corresponding transmission number in the third column. The fourth
through twelfth columns are time slots 1-0 of the frame. For
example, the first row indicates DL slot 1 is a dynamic allocation
of component carrier 3 for RU 1. DL slot 2 is a dynamic allocation
of component carrier 3 for RU 2. DL slot 3 is a dynamic allocation
of component carrier 3 for RU 3. Slot 4 is an UL slot and is,
therefore, blank. DL slots 5-6 are a dynamic allocations of
component carrier 3 for RUs 4 and 0, respectively.
[0082] FIG. 8B is a diagram showing the ordering
N.sub.RU.sup.A/N(n.sub.RU) of PDSCH ACK/NACKs of PDSCH
transmissions of RU, with RU index n.sub.RU reported in UL slot #4
for RU#1, where n.sub.RU=1 (without bundling) and RU#2, where
n.sub.RU=2 (with bundling) from the use case defined in FIG. 8A.
For example, DL slots 1 and 7 of the first row (secondary CC#3)
were allocated to RU 1, and their corresponding PUCCH indexes
n.sub.RU.sup.A/N(n.sub.RU=2) are all 1, since there is no bundling.
Thus, the ACK/NACK transmitted in response to DL slot 1 of the
first row represents reception only in that slot. DL slots 2 and 8
of the first row (secondary CC#3) and 3 and 9 of the second row
(secondary CC#2) were allocated to RU 2, and their corresponding
PUCCH ACK/NACK indexes n.sub.RI.sup.A/N(n.sub.RU=2) are all 1,
since there is bundling with a bundling factor of 4. This means
that if either slot 2 or 8 on secondary CC#3 or slot 3 or 9 on
secondary CC#2 fail to receive a transmission, therefore, a single
negative acknowledgement (NACK) signal is bundled and transmitted.
An acknowledgement (ACK) signal is transmitted only if all of slots
2 and 8 on secondary CC#3 and slots 3 and 9 on secondary CC#2
receive correct transmissions.
[0083] PUCCH allocation size is mainly driven by PDSCH ACK/NACKs.
PUCCH physical resource blocks (PRBs) are fully determined from the
UL/DL frame configuration, slot number, and maximum number of
supported RUs. As a result, the PUCCH allocation size does not need
to be explicitly signaled to the RUs. Furthermore, ACK/NACK
bundling is only required where there is a large difference between
UL and DL slots in a frame as in configuration 6 (FIG. 2). The
ACK/NACK window of FIG. 8B indicates a range of slots in a frame
where HARQ feedback signals may be bundled. The window spans both
time and component carrier (CC) frequency. The size of the window
depends on the TDD UL/DL configuration and UL slot number in the
TDD frame. The bundling factor within the window is the number of
RU feedback acknowledgement signals that are combined and
transmitted to the HU in a subsequent UL frame. This bundling
factor is signaled to the RU in the PBCH within the window. In
particular, the bundling factor in the PBCH defines the number of
consecutive bundled transmissions in an ACK/NACK report.
[0084] On the reverse side, UL transmissions from RUs to the HU are
also HARQ acknowledged by the HU. This is referred to as UL HARQ
ACK/NACK and the ACK/NACK reports are sent in downlink on the
Physical HARQ Indicator Channel (PHICH). Here as well, ACK/NACK
bundling, will be needed in some configurations. ACK/NACK bundling
of n transport blocks (TBs) into one ACK/NACK report consists is
transmitting ACK if all bundled TBs were correctly decoded (CRC
check passed) and NACK if at least one of the TBs had an incorrect
CRC.
[0085] When bundling 4 slots into 3, the first two UL slots (in
chronological order) are bundled together, the following two UL
slots are not bundled. Note slot bundling may bundle ACK/NACKs of
different RUs if different RUs were scheduled in the two slots.
Slot bundling applies between FDMA allocations of same FDMA index
n.sub.FDMA.sup.UL.
[0086] Referring to FIG. 9, there is a diagram showing non-adaptive
retransmissions having different allocation sizes through rate
matching. For example, a HARQ retransmission may have a different
allocation size than the initial transmission. Thus, it is rate
matched to the new allocation size and adjusted to the total number
of bits available for transmission in one transport block of the
new allocation. For UL and DL HARQ, the PDCCH tells in an
allocation grant if an UL or DL resource is preempted or replaced
by another RU. Preemption is signaled by a DCI bit associated with
the retransmission. The preempt bit is set to signal the format of
the retransmission even if the preempting RU is the same as the
preempted RU according to the following rules. When no RU is
scheduled in a dynamic or SPS allocation, the associated preempt
bit is reset. When no RU is scheduled in a dynamic allocation, the
associated DCI in the PDCCH is all zero (blank). When an RU is
scheduled in a dynamic allocation but reports a PBCH NACK, the
associated DCI in the PDCCH is all zero (blank) except for the
preempt bit which is set.
[0087] Embodiments of the present invention are directed to
synchronous Hybrid Automatic Repeat Request (HARQ) design for NLOS
backhaul. For each UL/DL configuration, there is a specific timing
and associated number of processes. For example, the diagram of
FIG. 9 is for UL/DL configuration 1 (FIG. 2). Slot numbers 0-9 at
the top show four sequential frames and four corresponding HARQ
processes. Frame boundaries at each slot 0 are shaded. In the
middle row of vertical arrows, a down arrow indicates a DL slot and
an up arrow indicates an UL slot. Lower curved arrows extend from a
DL slot to an UL slot that contains a corresponding ACK/NACK. Upper
curved arrows extend from the UL slot containing the ACK/NACK to a
subsequent DL slot that will include a retransmission in the event
of a NACK. The lower four rows represent four respective HARQ
processes which can be used by the same or different RUs. Each T
indicates a DL transmission on the PDSCH for the HARQ process in
that row. Correspondingly, each A represents an ACK/NACK on the
PUCCH for the HARQ process in that row.
[0088] There are several significant advantages to the foregoing
embodiments of the present invention. First, the HARQ is
synchronous and non-adaptive. A NACK implicitly dictates a
retransmission in the next available slot for that process. Second,
even though the retransmission is non-adaptive, it may have a
different allocation size than the original transmission. Third,
the different allocation size is rate matched to accommodate the
different allocation size. Fourth, the PDCCH tells in the
allocation grant if an UL or DL resource is preempted by another
RU. Finally, latency requirements are greatly reduced with respect
to LTE. HU processing for PUSCH reception and PHICH transmission
requires three slots or 1.5 ms. This is half that of LTE. HU
processing for PUCCH reception and PDSCH transmission requires two
slots or 1.0 ms. This is one third that of LTE. RU processing for
PHICH reception and PUSCH transmission requires two slots or 1.0
ms. This is one third that of LTE. RU processing for PDSCH
reception and PUCCH transmission requires three slots or 1.5 ms.
This is half that of LTE.
[0089] Still further, while numerous examples have thus been
provided, one skilled in the art should recognize that various
modifications, substitutions, or alterations may be made to the
described embodiments while still falling with the inventive scope
as defined by the following claims. Furthermore, embodiments of the
present invention may be implemented in software, hardware, or a
combination of both. Other combinations will be readily apparent to
one of ordinary skill in the art having access to the instant
specification.
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